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PREPARATION OF CAVITIES FOR PORCELAIN INLAYS 301
terial. The cavity form is the same as that just described for a
gold inlay.
Proximal Approach May be Used in this instance under some
conditions. The incisal approach may be used when excess sepa-
ration has been produced a little greater than the length of the in-
cisal line angle, as well as more than the thickness of the inlay
measuring from contact point to the greatest depth of the axial
wall, which permits the filling entrance from the incisal.
To Break the Cement Line on the Incisal Edge a rounded groove
Fig. 165. A Class Four, plan two, with double step for porcelain inlay.
should be made from the external end of the incisal line angle to
the incisal cavo-surface angle.
Plan Two, Class Four, is suitable for porcelain filling provided
the material will stand the strain at union of step and cavity
proper. The double step is advised. (Fig. 164.)
Plan Three, Class Four. The addition of the lingual step makes
many angle restorations with porcelain practical, as the tipping
strain can be well provided for by grooving in the lingual axial
wall next to the distal or mesial wall according to whether the
cavity is distal or mesial. The cavity should be so shaped that
the draw is directly to the incisal. The gingival wall should be
PREPARATION OF CAVITIES FOR PORCELAIN INLAYS 301
terial. The cavity form is the same as that just described for a
gold inlay.
Proximal Approach May be Used in this instance under some
conditions. The incisal approach may be used when excess sepa-
ration has been produced a little greater than the length of the in-
cisal line angle, as well as more than the thickness of the inlay
measuring from contact point to the greatest depth of the axial
wall, which permits the filling entrance from the incisal.
To Break the Cement Line on the Incisal Edge a rounded groove
Fig. 165. A Class Four, plan two, with double step for porcelain inlay.
should be made from the external end of the incisal line angle to
the incisal cavo-surface angle.
Plan Two, Class Four, is suitable for porcelain filling provided
the material will stand the strain at union of step and cavity
proper. The double step is advised. (Fig. 164.)
Plan Three, Class Four. The addition of the lingual step makes
many angle restorations with porcelain practical, as the tipping
strain can be well provided for by grooving in the lingual axial
wall next to the distal or mesial wall according to whether the
cavity is distal or mesial. The cavity should be so shaped that
the draw is directly to the incisal. The gingival wall should be
